The present invention relates to the art of earth boring and more particularly to rotary drill heads used in drilling oil and gas wells and the like.
The rotary drill head art is well developed. A rotary drill head is generally located below the rotary table of an oil well drilling rig. The drive kelly extends from the rotary table downward through the rotary drill head. A rotary swivel above the kelly allows drilling fluid to be pumped downward through the center of the kelly into the drill pipe and to the bottom of the borehole wherein it exits through nozzles in the drill bit and returns to the earth's surface in the annulus between the drill pipe and the wall of the borehole. Once the drilling mud is returned to the surface, it is processed to remove drill cuttings, debris and other materials such as gases entrained with the drilling mud. After processing, the mud is returned to the borehole through the drill string as previously described. It will be appreciated that a rotary seal must be provided to seal the annulus between the wall of the borehole and the rotating drill string. Rotary drill heads fulfill this function.
The rotary drill head must be rugged enough to withstand the high fluid pressures encountered during the drilling operation. A dynamic rotary seal must be provided and all of the foregoing must be accomplished while handling the highly abrasive and corrosive materials encountered during the drilling of the well. A further important requirement is that the entire system must be simple and easily repaired and/or replaced.
Rotary drill heads have traditionally used conventional packings and utilized the abrasive drilling fluid to energize the seal. Certain problems are encountered with such seals. When a pressure energized lip seal is used, the fluid being sealed normally leaks past the lip in infinitesimal amounts. In the case of a rotary drill head, when the abrasive drilling fluid leaks past the lip, both the seal and wear surface tend to be damaged. The present invention seeks to lengthen the life of the seals and wear surfaces of a rotary drill head. In the present invention the lubricant pressure energizes the lip seals rather than the drill fluid thereby excluding the abrasive drilling fluid from the seal area. Since the lubricant leaks past the lip seals no damage results to either the seal elements or the associated wear surfaces.